Lab scale salt caverns-first results on construction and investigation techniques

Abstract

Salt caverns from solution mining in bedded or domal saline structures are of increasing importance as temporary subsurface storage space to buffer fluctuating renewables and secure a stable energy supply. To assure the integrity of caverns during operation and long term abandonment, knowledge of geochemical rock-water interactions in the transition zone between cavity and salt rock is necessary. Due to the inaccessibility of cavern walls, a set of lab-based experiments were performed in hand-sized specimens by creating cm-sized cavities using fresh water injection and brine removal. The experimental simulations proved challenging and vacuum pressure tests revealed frequent leakage subsequent to borehole preparation. The samples were cut to expose the formed cavity and its margin. Micro X-ray Fluorescence mapping was employed to obtain information on element distributions and showed a clear separation between Na, Mg and K salt layers. XRF mapping represents a suitable technique to track spatial mineralogical changes related to rock-fluid interaction in salt rocks. Fluorescent liquids were used to visualize potential fluid pathways. First results show that these methods are promising in detecting geochemical changes and their extent and are, thus, useful tools in unravelling geochemical processes related to marginal areas of cavernous structures in salt deposits based on lab-scale simulations.